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CMU-900 used recently on new aircraft entered services after 2011, I don't blieve the plane in our case with MSN 28420 manufacured in 2002 will have CMU fitted?!

So even if they used the Honeywell CMU Mark III predecessor the principle is just the same.

If the ACARS and transponder were all managed through one CMU processor and that was overheating before take off (per ACARS R-channel signal evidence) then the question remains unanswered by your reply, just obfuscated.

I have learned by experience that when people try to deflect the question with an irrelevant objection it is usually because they are scared of the conclusion which the question leads to.

The answer obviously is if the ACARS and Transponder were all disabled by an overheating CMU unit regardless of manufacture and exact part number would this not suggest a different cause from criminal disabling of those systems?

So even if they used the Honeywell CMU Mark III predecessor the principle is just the same.

If the ACARS and transponder were all managed through one CMU processor and that was overheating before take off (per ACARS R-channel signal evidence) then the question remains unanswered by your reply, just obfuscated.

I have learned by experience that when people try to deflect the question with an irrelevant objection it is usually because they are scared of the conclusion which the question leads to.

The answer obviously is if the ACARS and Transponder were all disabled by an overheating CMU unit regardless of manufacture and exact part number would this not suggest a different cause from criminal disabling of those systems?

I wish to apologise for this old historical post. I was under a mistaken impression that the B777 used a CMU like the B767, however it got bashed into my skull outside this discussion that the B777 uses two AIMS cabinets.

Please can I ask a question about the Air Conditioning operation on a Boeing 777?
I am not an engineer.

I understand when there is electrical smoke in the MEC the override valve opens & Supply Duct pressure reverts to Ambient?

Does this imply that the entire cabin is then exposed to Ambient pressure?

I also understand that if there were an electrical failure causing the ELMS to shed power load then the CTC is supposed to close both upper & lower Pack Flow control & shut off valves?

Yet in the same (Lufthansa) QRH just a few lines further on I also read that when power fails, then air pressure pushes flow control and shut off valves to open?

This sounds like a contradiction?
I mean if the valves are unpowered and the MEC override valve is open then the aircraft wouldn't pressurize, right?

If there is ambient pressure in the Supply Duct at 35,000ft and no electrical power to the CTC Flow Control & shut off valves will that cause loss of cabin pressure?

If the MEC is open in override then wouldn't low duct pressure cause an alarm or am I missing something?
Would the engines still pushing bleed air to the ACM maintain duct pressure preventing or inhibiting an alarm?
Please can someone walk me through how the Low Duct Pressure alarm work or not work?

Wasn't there an AAD in 2008 when a B777 depressurized because the CTC was tricked somehow?

Why I am asking is this...

I have gotten to know some relatives of Capt Zaharie Ahmadshah. Late in 2016 they revealed to me that not only was it Zaharie's voice on the ATC audio recordings when MH370 reached cruise ALT, but also his voice was slurred. The Australians concluded for several reasons that the flight was characteristic of an unresponsive crew and a hypoxic flight. His sisters did not grasp the significance of his slurred voice when they described this to me and neither was i fishing for such advice.

As I recall his sister Dah Ah who fervently believes in hijacking was going on about the ATC recording being spliced from different recordings and how she though this must be some proof of cover-up of a hijacking. Then quite by chance she mentioned Zaharie spoke the last three times from MH370. I asked about that and then she added his voice was strange because it was slurred. I turned to elder sister Sakinab and asked is that true?

Sakinab confirmed it immediately. For a brief moment the conversation became quite excited from me. I had to explain to them why his slurred voice was relevant. I have always nurtured a belief there was some sort of electrical fire or failure etc. Australia's DSTG report from December 2015 cited evidence from the airline's attempts to send ACARS messages to MH370 every two minutes from 18:03 to 18:43 UTC that there was a prolonged failure of the Left AC Bus relay.

Thus I am trying to sketch out a scenario where overheating electricals in the MEC during the climb opened the override valve before communications were lost causing pilots to be in the early stages of hypoxia when some fault cased the Left AC Bus to fail?

I am assuming if for some reason pilots could not, or did not switch to using the Right IDG or APU that ELMS may have shed load taking comms with it?